Rainwater for washing machines and toilets can cut water consumption by 40 per cent

State of Green
By State of Green, May 29, 2020

Up to 10,000 Danish households’ washing machines and toilets will soon use rainwater instead of drinking water. This is estimated to cut water consumption by as much as 40 per cent.

Water resources worldwide are under strain. New solutions need to be tested and implemented to ensure that the next generation has better access to water. However, in the developed world water is being consumed indiscriminately. Therefore, in the newly constructed district Nye, which is a suburb of the Danish city Aarhus, rainwater will be used for toilet flushing and laundry. Up to 10,000 homes are planned to be built in the new district.

Most commonly in the developed world, we are washing our clothes and flushing our toilets with clean drinking water. However, using rainwater instead could cut drinking water consumption by as much as 40 per cent. It can also create a clear division between the essential drinking water and water used in everyday chores.

-Related solution: Rainwater Solution With Sustainable Multi Purpose

Purple pipes, an artificial lake and UV-disinfection

The solution is developed by the Danish water supplier Aarhus Vand in collaboration with Tækker Group, COWI, NIRAS, and Silhorko. The solution could be a vital part in the development of new sustainable districts throughout the world.

“We take the rainwater, which is collected in a lake that we have built, and clean it at the treatment plant. The treatment is done by a special ultrafilter and ultraviolet disinfection system, among other methods. We then send the water out into the homes via a separate pipe system we have developed for this purpose. The pipes are sized based on a calculation of the need for water for laundry and toilet flushing, and they are colored purple so that they are clearly different from the drinking water pipes. This will minimise the risk of malfunctioning,” explains Mariann Brun, Project Manager at Aarhus Vand.

The solution will also work in case of droughts. When there is insufficient rainwater available, the water supply is supplemented with wastewater from drains, which is also treated at the treatment plant. The entire infrastructure to direct the purified rainwater out to the residents of Nye has already been established. The purification plant itself is ready by the end of 2020.

-Related solution: Combined bicycle path for school kids and rainwater storage

Extreme rainfall and flood proof district

In addition to handling everyday rainfall, the district also deals with a rising threat of extreme rainfall due to climate change. Roads and paths are constructed to function as waterways, which should reduce the need for larger sewage pipes or delay pools during heavy rain.

“By using roads, paths and green areas to direct the water where it does the least damage, we handle extreme rain intelligently. We must not rely solely on laying pipes to alleviate extreme rain,” says Carsten Fjordback, Development Director at Cowi.

For example, roads direct the water to ball courts and parking lots designed to handle water in extreme quantities. Thereby, the solution combines water management with livability by using recreational spaces as flood protection.


Aarhus Vand (in Danish)

NIRAS (in Danish)

TV2 Øst (in Danish)


Photo: Aarhus Vand

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